By Wilson da Silva, Sydney
[Article Courtesy of New Scientist Magazine's Rex Files]
If you've ever wondered what colour the dinosaurs were, you won't have much longer to wait. Researchers in Australia have reconstructed the skin colours of ancient fish from fossils and say the technique will help to inject a little reality into reconstructions of other extinct animals.
'Colour reconstructions of extinct animals, such as the dinosaurs in Jurassic Park, are simply works of fiction,' says Andrew Parker, a biophysicist at the Australian Museum in Sydney.
Parker realised that the cell structures responsible for the iridescent sheen of tiny marine crustaceans called ostracods-a group of animals that has remained largely unchanged for the past 350 million years-are also present in fossils. These structures, called diffraction gratings, are microscopic patches of grooves, spaced so that they diffract light to give particular colours. In fossil ostracods, the diffraction gratings were slightly more primitive but served the same purpose.
This set Parker wondering whether the cellular structures responsible for colour in other living animals could be found in their ancient ancestors-perhaps allowing scientists to make a good guess at their colours.
When Parker looked at the well-preserved fossils of a number of marine animals, ranging from worms to fish, he found the same tiny structures on their spines and scales. He also identified other features responsible for colour: cells called chromatophores, which contain coloured pigments.
To his surprise, Parker even found the remnants of pigment in some of the better-preserved fossils. This allowed him to identify the chromatophores as black (melanophores), red (erythrophores) and silvery (iridophores). Many of these cells had survived in fossils because they were trapped within the bone as new layers of tissue were laid down during the animal's life.
In one ancient fish, a heavily armoured placoderm from the Devonian, some 370 million years ago, Parker and his colleagues found red pigment granules inside the chromatophores on the upper part of the body. They also recognised multilayered versions of the diffraction grating on the fish's belly. In modern fish, these diffract all wavelengths of light producing a silvery sheen. The placoderm, then, was probably red above and silver below.
Once they could recognise these structures, the team had little trouble reconstructing the colours of other extinct animals, says Parker. The chromatophores had probably been overlooked before because they resemble ordinary bone cells and are embedded in them. And the people who work on colour don't work on fossils, says Parker. If researchers know where to look and what to look for, they will be able to work out the colours of other extinct animals, including dinosaurs, he adds. 'We can finally accurately describe the colour of animals from the past rather than simply speculate or extrapolate the colour by comparing it to modern animals.'
New Scientist, 30 Aug 97, Volume 155, Issue 2097